Elastic resonator for timekeeping instruments



Dec. 8, 1970 w. R. BAUMGARTNER I 3,546,500

I I I ELASTIC RESONATOR FOR TIMEKEEPING INSTRUMENTS Filed Bay 27, 1969 ELECTRONIC DRIVE CIRCUIT 3,546,500 ELASTIC RESONATOR FOR TIMEKEEPING I INSTRUMENTS Werner R. Baumgartner, Bienne, Switzerland, assignor to Bulova Watch Company, Inc., New York, N.Y., a corporation of New York Filed May 27, 1969, Ser. No. 828,211 Claims priority, application Switzerland, May 29, 1968, 7,973/68 Int. Cl. H02k 33/02 US. Cl. 310-- 6 Claims ABSTRACT OF THE DISCLOSURE An elastic resonator of the tuning-fork type for timekeeping instruments, the resonator including a pair of tines extending from a common base, the tines in their static condition lying in a common plane. A weight is attached to the free end of each tine, driving means being provided to actuate the tines to effect push-pull oscillation thereof in directions normal to said common plane.

BACKGROUND OF INVENTION This invention relates generally to an elastic resonator for timekeeping instruments, and more particularly to a resonator constituted by two oscillating tines having Weights attached to their ends, the oscillation of the resonator being maintained by driving means generating electrical pulses. The resonator is therefore a tuning forklike device.

A fundamental problem which arises when producing electrical or electronic timekeeping instruments with a resonator, operating at an acoustic frequency, is the inexpensive manufacture of a resonator having a resonance frequency which is not excessively influenced by unavoidable manufacturing tolerances. Tuning forks are normally stamped or punched from a laminated metal sheet of definite thickness. However, this technically simple and very economical manufacturing method has a fundamental drawback.

The thickness of the tines, measured perpendicularly with respect to the plane for-med by both tines, is defined by the laminating procedure and is therefore very accurate. On the other hand, the width of the tines depends on the wear of the punching tools. Since the frequency depends on the width of the tines by the third power of its square root, a very small degree of wear in the punching tool will give rise to an appreciable departure of the resonance frequency of the punched-out forks with respect to the theoretical value of the resonance frequency.

Attempts have heretofore been made to avoid this drawback by bending the fork from a previously stamped-out .steel band. This inaccurate manufacturing method leads to shape errors which cannot be corrected by the symmetrization of the fork. Such forks can be used for table clocks, wall clocks, alarm clocks, etc. but they are not suitable for Wristwatches of high accuracy, where losses must be kept to a minimum.

BRIEF DESCRIPTION OF THE INVENTION In view of the foregoing, it is the main object of this invention to provide an elastic resonator or tuning-fork device whose resonance frequency is substantially independent of the wear of the punching tool used in fabricating the device. Moreover, the resonator is free of shape errors which result from bending the tines after stamping.

A resonator according to the invention is characterized by the fact that both tines thereof oscillate in a pushpull manner in directions which are perpendicular to the Unlted States Patent Oflice Patented Dec. 8, 1970 plane defined by both tines. The driving means for the tines may include an element fixed on the tine, or they may be fixed partly on the tines and partly on the pillar plate. These means may be of the electromagnetic, electrodynamic or piezoelectric type, or these means may even be predicated on another principle. Suitable electromagnetic transducers for this purpose are disclosed in United States Pats. 3,221,190, 2,971,323 and 2,960,817.

In a resonator according to the invention, the resonant frequency is primarily defined -by the thickness of the metal sheet which is used for its manufacture, the resonator comprising two tines and a common base. Since the frequency of the fork is proportional to the square root of the width of the tines, the resonance frequency changes only slightly when the punching tools wear out.

BRIEF DESCRIPTION OF DRAWING part, in order to more clearly illustrate the shape of the resonator.

DESCRIPTION OF INVENTION FIG. 1 shows an oscillator in accordance with the invention without weights attached thereto. It consists of a tine 1, a tine 2, and a base 3 which is common to both tines 1 and 2 as well to a mounting stem 4. Stem 4 is secured to a base plate by means of screws 5 and 6. The fork is preferably punched out from a laminated sheet of metal, various alloys being suitable for this purpose. The thickness of the sheet corresponds to the thickness of the tines. The width of the tines is indicated by letter b. Normally, width b is larger than the thickness d, in order to suppress parasitic oscillations.

Tines 1 and 2 in their static condition lie in a common plane. The normal oscillation mode of the tines 1 and 2 is a push-pull movement which is perpendicular to this common plane. That is to say, if tine 1 moves in direction A, tine 2 will move in the opposing direction A. On the other hand, when tine 1 moves in direction B, tine 2 will move in the opposing direction B.

In the embodiments of of FIGS. 2 and 3, tine 1 carries a stiff arm 7 which is L shaped, the connecting link of said arm being perpendicular to the common plane of tines 1 and 2, the extension of said arm being parallel to tine 1 and extending in the opposite direction with respect to the free end of tine 1. Tine 2 also bears a stiff arm 8, which arm is located on the other side of the common plane of both tines. To the free end of time 1 there is attached a cup magnet 9 of known shape, whereas the stiff arm 7 bears a counterweight 11 at its free end. At tine 2, the arrangement is reversed, the free end of tine 2 bearing a weight 10 and the free end of stiff arm 8 bearing a cup magnet 12 acting as a counterweight. The cup magnets cooperate with fixed transducer coils in the manner disclosed in the above-identified patents.

Since both cup magnets 9 and 12 are parallel to each other and are open in the same direction, one realizes a fundamental advantage therefrom. It is possible to disassemble the resonator from the base plate without being required to disassemble the transducer coils and electronic components. Assembly and service of the timepiece are therefore facilitated.

It is advantageous to so choose the weights and the counterweights of tines 1 and 2 and stiff arms 7 and 8 as to have the common center of gravity of the weight and the corresponding counterweight located on the common axis of rotation of both tines. This leads to a marked reduction in the frequency error which is present in conventional tuning forks, depending on their attitude in a gravity field. It is also advantageous that all four centers of gravity of cups 9 and 12 and counterweights 10 and 11 are situated in one plane which is perpendicular to the plane common to both tines and that these elements are symmetricaly arranged with respect to said tines.

The invention may be realized in other embodiments. For example, both times could be fitted with cup magnets or both tines could be fitted with Weights, the cups then being fixed at the free ends of the stiff arms. It is even possible to have only one extremity fitted with a cup magnet, the three others bearing weights or counterweights.

While there has been shown and described a preferred embodiment of elastic resonator in accordance with the invention, it will be appreciated that many changes and modifications may be made therein without, however, departing from the essential spirit of the invention.

What I claim is:

1. An elastic resonator for timekeeping instruments, said resonator comprising:

(A) a pair of tines extending from a common base, said tines in their static condition lying in a common plane,

(B) a weight attached to the free end of each tine,

(C) driving means to actuate said tines to effect pushpull oscillation thereof in directions normal to said common plane,

(D) a stiff arm attached to each tine at a point adjacent the free end thereof, and

(E) a counterweight secured to each arm and so disposed as to locate the common center of gravity of said weight and counterweight close to the common axis of rotation of both tines, the stiff arms bearing said counterweights lying on opposite sides of said common plane.

2. An elastic resonator as set forth in claim 1, wherein at least one of said weights forms an element of said driving means.

3. A resonator as set forth in claim 2, wherein at least one of said counterweights constitutes an element of said driving means.

4. A resonator as set forth in claim 1, wherein the weight on one tine and the counterweight on the stiff arm attached to the other tine are cup magnets which are open to the same side and are parallel to each other, said cup magnets cooperating with fixed coils which are concentrically disposed with respect to said magnets.

5. A resonator as set forth in claim 4, wherein the cup magnets are so arranged that they are displaced the same distance from said common plane and are perpendicular thereto.

6. A resonator as set forth in claim 5, wherein the center of gravities of the weights on the tines and the counterweights on the arms lie in a plane perpendicular to said common plane and are symmetrically disposed relative to said tines.

References Cited UNITED STATES PATENTS 3,447,311 6/1969 Beyner et al. 58--23 3,281,725 10/1966 Albsmeier 333-72 2,960,817 11/1960 Hetzel "58-23 2,888,582 5/1959 Hetzel 310-25 3,303,705 2/1967 Dostal 84409X I FOREIGN PATENTS 6,709,050 3/ 1968 Netherlands 58-23 451,021 l/ 1968 Switzerland 5 823 1,130,012 10/ 1968 Great Britain 58-23 MILTON O. HIRSHFIELD, Primary Examiner B. A. REYNOLDS, Assistant Examiner US. Cl. X.R. 58-23; 84-409 

